1. Field of the Invention:
This invention relates to a tree pruning machine for cutting branches of a standing tree while climbing the tree and, more particularly, to a tree pruning machine of the type wherein a sensor detects a branch contacting the top of a cutting unit and prevents the top of the cutting unit from being interposed in the branches by temporarily stopping the drive of the elevating wheels.
2. Description of the Relevant Literature:
As shown in FIG. 23(a), a tree pruning machine a has a body b and a cutting unit c carried on the body b. By driving elevating wheels e with an engine d, the pruning machine a spirally climbs the tree T and cuts branches t with cutting unit c. The branch cutting force of the center cl of the cutting unit c is relatively large, but the branch cutting force of the top c2 of the unit c is small. When the branches are being cut by cutting c, a branch t tends to frequently make contact with the top c2 of the unit c. In this case, the top c2 may simply cut the branch t, but since the cutting force of the top c2 for cutting the branch t is small, the top c2 frequently is unable to cut the branch t.
FIG. 23(b) illustrates a situation where the top c2 of the cutting unit 2 cannot cut the branch t as described above. When the top c2 of the unit 2 contacts the branch of t, and the lower portion of the branch t is cut, branch t moves downwardly by its own weight as designated by chain lines, and the top c2 is pressed strongly between the cut portions of the branch t so that the branch t cannot be cut or the load on the engine d becomes excessive and causes the engine to stop. If the top c2 of the cutting unit 2 becomes jammed between the branches t so that the pruning machine cannot continue climbing the tree T, the wheels e may continue to rotate while maintaining contact pressure with the surface of the tree T and damage the bark of the tree T.